Metastasis-directed ablative radiotherapy in castrate-resistant oligometastatic prostate cancer: A retrospective study of 8 high-volume French centers from the COLib (Cercle des Oncologues Liberaux).

152 Background: In castrate-resistant oligo metastatic prostate Cancer (CRoligoMPC), the benefit of metastases-directed ablative radiotherapy (MDRT) is poorly investigated. Our study retrospectively reviewed the cases of CR oligoMPC treated with MDRT. Methods: Patients receiving MDRT in CRoligoMPC were retrospectively reviewed. Patients were included if: they had < 5 metastases on metabolic work-up, testosterone is < 50 ng/mL, metastases received MDRT. Patients and disease's data were collected: age, Gleason score, time to metastases, time to castration resistance; medical treatments, metastases location (bone versus node); radiotherapy regimens, PSA (PSA doubling time PSADT at the time of MDRT and PSA response). Progression was assessed according to PCWG criteria. PFS and OS are defined as the time from MDRT to first progression, for PFS and death date for OS. Kaplan-Meier analysis was used to summarize time-to-event variables and curves were compared with the log-rank test. A logistic regression was used to identify predictive factors of PFS. Results: the median follow up is 25.6 months.107 patients met inclusion criteria, among those 197 metastases received MDRT. Median age at MDRT time was 73 years. Median hormonosensitivity duration was 38 months (4-225). Forty six patients had metastases at the time of hormonosensitivity and 61 developed metastases in the castration resistance (CR)period (spartan-like population). PSA doubling time at the time of MDT RT was < 12 months in 88%. A median number of 2 metastases per patient was treated (1-4), 54% had RT on bony metastases only, 38% on nodes, 8% on bone + node. In 61 patients with metastases at the time of CRPC, 34.5% received a CR systemic medication before or concomitantly to MDRT, 39% received CR medication at progression, 23.5% never received CR treatment (unknown in 3%). OS is 93% at 2 years and 81.4% at 3 years. For node-only metastases, 2y OS is 100% versus 89% for bone metastases. Median PFS is 12.6 months (IC 95% [9.6; 17]). Metastases location, grade group, PSA or hormonosensitivity duration were not related to PFS in a univariate survival analysis. PFS was 10.2 months when PSA Doubling time was < 6 months, versus 18.2 months when it exceeded 6 months (NS). The PSA 50% response was studied in the Spartan like population, it was 83.4% in patients receiving MDRT AND new generation hormonotherapy; 31% in those who received MDRT without new generation hormonotherapy, and 20% in those who received MDRT at the time of progression of oligometastases occurring under new generation hormonotherapy. Conclusions: In a population of CR oligoM PC with short PSA DT, MDRT leads to a PFS of 12.6 months and to a 3y OS of 81.4%. In this setting, androgen receptor targeting agents are the standard of care. Whether adding MDRT could improve prognosis should be prospectively evaluated.